The periodic impact responses and stability of a human body in a vehicle traveling on rough terrain

The periodic impact motions of passengers in a vehicle traveling on rough terrain are investigated through a linear model of vehicle and passenger systems. In this mechanical model, the human body is considered as a massless bar with a lumped mass. The linear model assumes that the motion response of vehicle is quite small compared to the passengerʹs pitch motion since the vehicle chassis has a quite large mass and large moment of inertia compared with each passenger. The period-1 motion pertaining to two impacts, respectively, on two walls during N-periods of the ground motion is predicted analytically and numerically. The stability and bifurcation of such a period-1 motion are determined. The impact motion becomes complicated with increasing ground motion amplitude, but the impact motion reduces with increasing torsional damping. Although the mechanical model used in this paper is an ideal one, the dynamic responses of the human body in vehicle traveling on rough terrain is useful for the rough evaluation of the human body safety in traveling vehicles.